The invention relates to manufacture of equipment for sewing, sewing industry, knitted goods industry, leather industry, and shoe industry, in particular shoe double-thread chain-stitch sewing machines.
A sewing machine is known which makes a double-thread stitch line of the type 401 (see Reibarkh L. B., Reibarkh L. P., Dremalin N. A. "Sewing Machines for Knitting & Textile Industry", M., "Legprombitizdat", 1989, pages 33-56), which is formed with a needle and one looper with needles in them, in which the looper performs a complicated spacial movement including an oscillating movement transversely to the line of stitch in a vertical plane and a reciprocating movement along the line of stitch in a horizontal plane.
The formation of a stitch is performed in the following sequence. A needle with a top thread pierces through a material and passes through it a loop of the top thread. During lifting of the needle from its extreme lower position above its ear a loop-overlap of the top thread is formed, and the looper is inserted with its nose into the loop-overlap during its oscillating movement through the left in the vertical plane. The loop engages the top thread. During a further movement through the left, the loop expands the loop of the top thread, introduces into it a loop of the bottom thread and deviates in a direction, which is opposite to the direction of movement of the material, by a value which insures the position of the looper before the needle. The needle lifts and leaves the loop of the top thread on the looper, it exits the material and starts lowering when it reaches an extreme top position. During the location of the needle outside the material, the material is displaced by the value of the stitch. The needle during a second lowering pierces the material and passes the loop of the top needle through it. At this time the looper must start its movement to the right so that on the one hand it provides the positioning of the loop of the top thread fitted on it at the right side of the needle, and at the other end the lower thread of the looper remains still at the left side of the needle. Therefore under the needle a kind of a triangle with an apex in the point of the preceding piercing end sides composed of the top needle, lower needle and the body of the looper is formed. The needle must reach (pierce) in the area of this triangle, since otherwise the stitch is missing. After piercing the needle continuous lowering and passes the loop of the top needle through the loop of the bottom needle. The looper during the movement to the right throws the loop of the top thread to the lower thread of the looper. The loop of the top thread which is thrown from the looper is reduced by a lowering needle, and a preliminary tightening of the stitch by the needle is performed, while the looper continues its movement to the extreme right position and deviates also in direction of movement of the material. The needle reaches its extreme bottom position, and then lifts so as to form a loop-overlap of the upper thread, and the looper engages it during movement. The final tightening of the stitches performed by joint action of the looper and mechanism of movement of the material.
In the above mentioned machine, the mechanism of the looper is complicated in the sense of construction, and also the stability of operation of the machine requires a great area of the triangle, which depends from manufactures. Moreover, the formation of the stitch, or in other words weaving by the top and bottom threads though occurs over one revolution of the main shaft, but the final tightening of the stitch is performed not immediately, but at the second-third cycle depending on a thickness, physics-mechanical properties of the material, a pitch of the stitch and required value of tightening of the stitch with the participation of practically all working units of the machine. The produced stitch is easily unraveled from the end under a relatively low load applied to the bottom thread, which negatively affects a quality of the stitch.
Also, a sewing machine is known, which makes a double-thread stitch line of the type 401 with an increased spreading of the stitch (see Polukhin V. P., Reibarkh L. B. "Stitch line sewing machines of foreign firms", M., "Light industry", 197, pages 114-163).
The working units of the machines are: a needle, a looper, an expander, a toothed rack for moving of the material, a pressing leg, a needle plate with a slot, cutters for cutting of threads, and a device for supplying threads. In contrast to the previous machine, also the expander participates in the process of loop-forming and it moves in a horizontal plane. It contributes to the formation of a stable triangle of threads, pulling the bottom thread of the looper and a branch of the top needle thread in direction of movement of the material. In addition to this, the machine also fixes the stitches by a reverse seam. Both during the direct as well as the reverse movement of the material, due to the pulling by the expander of the bottom and top threads, a stable triangle is formed between the looper, its lower thread, and the loop of the upper needle thread. In order to improve tightening of the stitch during the reverse movement of the material, an additional regulator for tightening of the top thread is installed on the machine, and it is activated only during the reverse movement of the material. The structure of the stitches obtained on the machine is different from the structure of common double-thread stitch lines of the type 401, in that the loop of the upper needle thread extends along the line in direction toward a next stitch. Such a line has an increased spreading up to 60%, and therefore the machine is used in a leather goods industry and sewing industry for processing of materials having an increased elasticity.
However in this machine the mechanism of looper is complicated in the structural sense. The participation of the expander in the process of forming of the stitch also complicates the construction of the machine. Moreover, the fixation of the line with a reverse seam which is performed with the use of additional devices does not provide a complete non-unraveling of the line from the end, but only complicates the unraveling of the line. The formation and tightening of the stitch is performed during the second-third cycle with participation of actually all working units of the machine, which reduces the reliability of the operation.